linux-kernel - Re: get_vmalloc_info() and /proc/meminfo insanely expensive

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Message-ID: <CA+55aFzh--4diDL5GutA_B7vGhjx03KLnYMWLc4KZPo_UqAwOA@mail.gmail.com>
Date:	Thu, 13 Aug 2015 15:56:07 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Tony Luck <tony.luck@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: get_vmalloc_info() and /proc/meminfo insanely expensive

On Thu, Aug 13, 2015 at 2:15 PM, Tony Luck <tony.luck@...il.com> wrote:
>
> could you at least care enough to write that as
>
>       if (time_after(now, last + HZ)) {

Absolutely not. That would be wrong.

"time_after()" covers half the "unsigned long" space (very much on
purpose). We want the cached case to trigger _only_ for the much
tighter case of exactly 1000 jiffies.

                 Linus
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